1. Field of the Invention
The present invention relates to a printed-wiring board having a plurality of columns of wiring patterns formed by screen printing and more particularly to a printed-wiring board in which deviation of pattern is adapted to be effectively detected.
2. Description of the Prior Art
In the manufacture of printed-wiring boards by screen printing, holes for through-hole connection are made in the board with the surface of the hole plated with copper, a plurality of columns of circuit patterns are printed on both front and rear surfaces, and copper on the unnecessary portions other than the circuit patterns are removed by etching. Then, a mask pattern formed of a resist layer is printed on the board, reference holes for punching work are made therein, and then a plurality of printed-wiring boards are obtained by punching work.
With such printed-wiring boards manufactured by the screen printing method, there is a problem that expansion or shrinkage of the screen affects the dimensions and accuracy of the wiring pattern.
When such a screen printing method is used, the screen easily expands or shrinks due to changes in the temperature and humidity, or the screen becomes expand as it is used many times. Thus, deviation of the pattern is easily produced particularly in the type of screen having a plurality of columns of wiring patterns.
Further, in the case where a plurality of wiring circuit patterns having circular arc patterns are arranged on a printed-wiring board by the use of the screen printing method and the outer circumference of the product region corresponding to each wiring circuit pattern and the central portion of the circular arc pattern are punched so that the product is cut out to be concentric with the circular arc pattern, deviation the circular arc pattern with respect to the center of the circular arc is liable to be produced in the product.
In the past, the deviation of the pattern due to expansion of the screen was checked by visual inspection of the operator so that the screen producing large deviation of the pattern was replaced with new one, However, since there was no means to accurately determine occurrence of the pattern deviation by visual inspection, it was often the case with such a prior art method that the time to replace the screen was lost and the use of the expanded screen was continued even when the pattern deviation exceeded its allowable limit, and therefore, there was a problem that a large number of defective products were produced.